RCW6%20solutions

RCW6%20solutions - Physics 204, morning summer 2008...

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Physics 204, morning summer 2008 Recitation ClassWork 6 solutions Chapter 21 Conceptual Questions #14 17 Concepts & Calculations #81,84,85 14 . REASONING AND SOLUTION The drawing shows an end- on view of three parallel wires that are perpendicular to the plane of the paper. In two of the wires, the current is directed into the paper, while in the remaining wire the current is directed Current out of the paper. The two outermost wires are held rigidly in place. From Example 8, we know that two parallel currents that point in the same direction attract each other while two parallel currents that point in opposite directions repel each other. Therefore, the middle wire will be attracted to the wire on the left and repelled from the wire on the right. Since each of the fixed wires exerts a force to the left on the middle wire, the net force on the middle wire will be to the left. Thus, the middle wire will move to the left. 15 . REASONING AND SOLUTION The figure below shows the arrangements of electromagnets and magnets. N S N S N S N S (b) (a) We can determine the polarity of the electromagnets by using RHR-2. Imagine holding the current- carrying wire of the electromagnet in the right hand as the wire begins to coil around the iron core. The thumb points in the direction of the current. For the electromagnet in figure ( a ), the fingers of the right hand wrap around the wire on the left end so that they point, inside the coil, toward the right end. Thus, the right end of the coil must be a north pole. Similar reasoning can be used to identify the north and south poles of the electromagnet in figure ( b ). The results are shown in the figure above. Since the like poles of two different magnets repel each other and the dissimilar poles of two different magnets attract each other, we can conclude that in both arrangements, the electromagnet is repelled from the permanent magnet at the right. 16 . REASONING AND SOLUTION The figure below shows the arrangements of electromagnets.
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We can determine the polarity of each electromagnet by using RHR-2. Imagine holding the current- carrying wire of the electromagnet in the right hand as the wire begins to coil around the iron core.
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RCW6%20solutions - Physics 204, morning summer 2008...

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